A blood vessel can be any vascular structure, e.g., an artery, a vein, or a capillary. A dilated or malformed vein can be associated with one or more of a variety of disease conditions such as, e.g., port wine stains and varicose veins.
Port wine stains can include post-capillary venules. Port wine stains can begin in infancy, and may both thicken and darken in color with time. In addition to being disfiguring, port wine stains can have adverse psychosocial effects. A conventional treatment for port wine stains may use a pulsed dye laser at a wavelength of 595 nm. A success rate for complete clearance of port wine stains may be low when using conventional treatment modalities such as the 595 nm pulsed dye laser, which can result from inadequate depth of penetration. Deep vessels can be targeted using, e.g., a 1064 nm Nd:YAG laser treatment for port wine stains. However, a wavelength of 1064 nm can be more strongly absorbed by arterial blood (which may contain primarily oxygenated hemoglobin (“HbO2”)), than by venous blood (which may contain a mix of deoxygenated hemoglobin (“Hb”) and HbO2)). Thus use of the Nd:YAG laser to treat port wine stains may create undesirable arterial damage, causing tissue necrosis and scarring, and can be dangerous to a patient. Although radiation from a 595 nm pulsed dye laser may be somewhat more absorbed by deoxygenated hemoglobin (Hb) than by oxygenated hemoglobin (HbO2), treatment fluence with the pulsed dye laser can still be limited by potential thermal damage to arteries. It may be desirable to have a laser that is designed specifically to target deoxygenated hemoglobin (Hb), and can be significantly more selective for veins.
Varicose veins can be dilated, tortuous veins which may result from defective structure or function of the valves of the veins, from intrinsic weakness of a vein wall, or from arteriovenous fistulas. Varicose veins can be categorized as superficial or deep. Superficial varicose veins may be primary, originating in the superficial system, or secondary, resulting from deep venous insufficiency and incompetent perforating veins, or from deep venous occlusions causing enlargement of superficial veins that can serve as collateral veins.
Superficial varicose veins may provide an undesirable cosmetic appearance. Conventional treatments for superficial varicose veins can include sclerotherapy or surgical therapy. For example, sclerotherapy can include injection of a sclerosing solution such as hypertonic saline or surfactants into blood vessels of interest, which may result in deformation of the vascular structure. Surgical therapy can involve extensive ligation and stripping of greater and lesser saphenous veins. However, an administration of such therapies can use a high degree of technical skill. Also, a fear of needles and/or surgical procedures may prevent many patients from seeking these treatments.
Lasers and other light sources can be used in photothermolysis therapy to treat dilated blood vessels, such as superficial varicose veins. Photothermolysis treatment techniques are described, e.g., in U.S. Pat. No. 5,558,667. Absorbed light, which can be provided in a form of pulses, may be used to damage the vessels while sparing surrounding tissues. For example, an irradiation of a blood vessel with an electromagnetic radiation can lead to an absorption of energy by blood components contained therein and subsequent heating of the vessel. The heated vessel may thrombose and collapse, which can produce desired therapeutic effects for treatment of venous malformations. However, nearby arteries may also be damaged by such photothermolysis techniques, which can lead to partial or complete closure of the arteries, necrosis of adjacent tissue, and unwanted scarring.
A reperfusion of treated blood vessels may reduce the effectiveness of photothermolysis treatment. Multiple treatments can be preferred because of the reperfusion of a treated vessel, which can become more likely if the amount of applied energy is limited to avoid unwanted damage to nearby arteries. High costs, number of treatments, and risk of post-treatment pigmentation are other negative factors which may be associated with photothermolysis therapy.
Superficial varicose veins may be treated using sclerotherapy, which can be effective but is often painful, and can have side effects including, e.g., hyperpigmentation, matting, and/or ulceration. Various lasers may be used for treating ectatic leg veins such as, e.g., a pulsed dye laser operating at a wavelength of 595 nm, an alexandrite laser at 755 nm, a diode laser at 800/810 nm, or a NdYag laser at 1064 nm, although the use of such lasers may not be very effective and/or may produce undesirable side effects. A phototreatment of veins using lasers or other sources of electromagnetic radiation such as, e.g., Intense Pulsed Light (“IPL”) sources, may also induce unwanted thermal damage to nearby arteries.
Therefore, it may be desirable to provide a laser or IPL source that can selectively photocoagulate veins for treatment of various venous malformations, with relative sparing of arteries.